Porous cement film and preparation method thereof

Abstract

The invention relates to the field of cement films, in particular to a porous cement film and a preparation method thereof.The porous cement film is prepared from raw materials including a functional modified polymer, a dispersing agent, a binding agent, cement and water; the functional modified polymer is a polymer containing quaternary ammonium salt cations, a phosphate group and a chitosan structure, the functional structure is introduced through a chemical means, excellent hydrophilicity, antibacterial property, cation adsorbability and antistatic property are achieved, and meanwhile the problem of mechanical property difference caused by a traditional physical blending mode is avoided.

Description

Technical Field

[0001] This application relates to the field of cement membranes, and more specifically, to a porous cement membrane and a method for preparing the same. Background Technology

[0002] Membrane separation technology is widely used in the water treatment industry, such as seawater desalination and wastewater treatment, due to its advantages such as high efficiency, high integration, and no phase change. Its main component is the separation membrane, which can be divided into two main categories based on materials: organic membranes and inorganic membranes. Organic membranes dominate the market due to their simple preparation process and low cost. However, limited by the physicochemical properties of the materials, they are prone to membrane structure damage, rapid fouling, and filtration performance failure when treating highly polluted, corrosive, or high-temperature solutions, leading to reduced operating efficiency. Inorganic membranes are mainly ceramic and metal membranes, which have advantages such as high temperature resistance, high mechanical strength, and strong chemical stability. However, their preparation process requires high-temperature calcination, resulting in high membrane brittleness and excessively high energy consumption during preparation.

[0003] Porous cement membranes are a novel type of membrane material used for liquid separation, forming directional channels within a cement matrix. They are made from cement powder, a pore-forming agent, and a binder. The process involves first crystallizing the pore-forming agent through directional freezing, then removing the crystals via vacuum drying to form the directional channel structure, and finally curing the cement structure. This method offers advantages such as abundant raw material resources, stable properties, high-temperature resistance, resistance to organic solvents, corrosion resistance, simple processing, controllable pore structure, and no need for high-temperature calcination. During the freeze-forming process, the pore-forming agent grows directionally under the influence of a temperature gradient, and after vacuum drying, it forms a specific pore structure. Therefore, the pore-forming agent and the temperature gradient are the main influencing factors on the pore structure.

[0004] Researchers have been dedicated to developing a novel membrane product that combines the advantages of both inorganic and organic membranes. Traditional cement membrane materials suffer from poor hydrophilicity, susceptibility to biofouling, and insufficient mechanical properties in water treatment and pollution remediation. For example, patent CN103739306A describes a method for preparing directional porous cement using ball milling, mechanical stirring, directional freeze casting, freeze drying, and constant temperature and humidity curing. After prolonged operation, fouling (especially organic fouling) easily clogs the pores of directional porous cement materials, leading to performance degradation. Chemical cleaning is necessary, which not only damages the membrane structure to some extent but also releases the cleaning chemicals and fouling into the environment, causing pollution and resource waste. While introducing additives through physical blending can improve some properties in existing technologies, it often results in significant differences in mechanical properties and poor stability. Therefore, developing a novel cement membrane material that combines hydrophilicity, antibacterial properties, adsorption properties, and mechanical strength is of great significance. Summary of the Invention

[0005] This application provides a porous cement membrane and its preparation method. This application introduces functional structures through chemical means, which have excellent hydrophilicity, antibacterial properties, cationic adsorption and antistatic properties, while avoiding the mechanical property differences caused by traditional physical blending methods.

[0006] In a first aspect, this application provides a porous cement membrane, employing the following technical solution: A porous cement membrane is provided, wherein the raw material of the porous cement membrane is composed of a functional modified polymer, a dispersant, a binder, cement, and water; the functional modified polymer is a polymer containing quaternary ammonium salt cations, phosphate groups, and chitosan structures; and the cement membrane has an oriented lamellar pore structure.

[0007] By adopting the above technical solutions, this application introduces a variety of functional structures through the addition of functionally modified polymers. Specifically, the expansion of the branched structure of the polymer by the phosphate groups significantly reduces the water contact angle of the material and improves its hydrophilicity. Furthermore, the phosphate groups and the chitosan quaternary ammonium salt structure endow the material with antibacterial, cationic adsorption, and antistatic properties. In addition, the phosphate groups react with calcium ions (Ca) in cement... 2+ This process forms complexes, regulates the cement hydration process, and optimizes the formation of porous structures and mechanical properties. Furthermore, by introducing various functional groups through the functionally modified polymer method described in this application, the resulting cement membrane material exhibits minimal differences in mechanical properties and excellent stability.

[0008] Furthermore, the cement membrane of this application has an oriented lamellar pore structure, which macroscopically exhibits high barrier properties, high strength, high toughness, and high durability. The oriented lamellar pore structure of this application originates from the combined effect of the cement hydration process and the material self-assembly behavior, specifically based on the following principles: (1) Directional growth in confined space: In the complex system of cement paste, which is full of tiny particles and limited water, the crystal growth space of cement hydration products (such as ettringite, CSH gel, etc.) is limited. They tend to grow and arrange themselves in the narrow gaps between particles along the direction of least resistance, thus naturally forming a preliminary microstructure with a certain orientation. (2) Template effect and self-assembly: This is the key to forming a highly ordered lamellar structure. The added functional polymers will spontaneously aggregate in the alkaline and ionic environment of cement paste to form lamellar micelles, vesicles or liquid crystal phases. These polymer aggregates are like "templates", guiding the growth and deposition of cement hydration products on their surface or between layers. The hydration products "replicate" the lamellar structure of the template, and finally leave behind oriented lamellar channels after the template decomposes or stabilizes. (3) Intrinsic morphology of hydration products: The main hydration product of cement, CSH gel, itself has a nanosheet or fibrous micromorphology. Under the regulation of functional polymers, these intrinsically sheet-like structural units can be stacked more orderly, rather than cross-linked together randomly.

[0009] Therefore, the formation of the oriented lamellar pore structure in the cement membrane of this application is a typical process combining "natural growth" and "artificial induction." The intrinsic properties of cement hydration products provide the basis for the formation of the lamellar structure, while the addition of functionally modified polymers is the key to achieving a highly ordered, regularized structure and optimized performance. Through careful design and selection of polymers, the final microstructure and macroscopic properties of cement-based materials can be precisely controlled, much like "programming," thereby meeting the needs of various demanding engineering applications.

[0010] Further, the mass ratio of the functional modified polymer, dispersant, binder, cement and water is (7~8):(0.3~0.8):(0.1~0.7):(50~60):(30~42).

[0011] Furthermore, the preparation method of the functional modified polymer includes the following steps: Tertiary ammonium acrylates are quaternized with haloacids to generate quaternary ammonium salt cationic monomers containing carboxyl groups. Esterification reaction of quaternary ammonium salt cationic monomers containing carboxyl groups with chitosan produces compounds containing both quaternary ammonium salt cationic and chitosan structures. Compounds containing quaternary ammonium salt cations and chitosan structures are phosphorylated with phosphorus pentoxide and methanesulfonic acid to generate functionally modified polymers.

[0012] Furthermore, the preparation method of the functional modified polymer includes the following steps: In anhydrous ethanol, tertiary ammonium acrylates and halo acids are quaternized in proportion. After reacting at 45-75℃ for 4-8 hours, the mixture is cooled to room temperature, the solvent is removed, and the mixture is washed and dried to obtain a quaternary ammonium salt cationic monomer containing a carboxyl group. A quaternary ammonium salt cationic monomer containing a carboxyl group was mixed with 1,2-dichloroethane, and hydrogen chloride gas was introduced. The mixture was reacted at room temperature for 0.5-4 hours. Chitosan was then added to the above reaction mixture, and hydrogen chloride was slowly introduced. The mixture was heated to reflux, and the azeotrope of dichloroethane and water was distilled off at 45-83°C. The mixture was separated into layers in a water separator, and the lower layer of 1,2-dichloroethane was added back into the reaction system. The reaction was completed in 4-8 hours. The mixture was cooled and filtered, and the filter cake was recrystallized to obtain a compound containing quaternary ammonium salt cationic and chitosan structures. A compound containing quaternary ammonium salt cations and chitosan structure was added to methanesulfonic acid. Then, phosphorus pentoxide was added under reaction conditions of 0-5°C, and the reaction was mechanically stirred for 2-4 hours under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether, washed, filtered, and vacuum dried at 60-80°C for 12-24 hours to obtain the functional modified polymer.

[0013] Furthermore, the tertiary ammonium acrylate is dimethylaminoethyl acrylate, propyl 3-(dimethylamino)acrylate, or butyl 3-(dimethylamino)acrylate; the haloacid is bromopropionic acid, bromobutyric acid, chloropropionic acid, or chlorobutyric acid.

[0014] Further, the binder is at least one of polyvinyl alcohol, carboxymethyl cellulose, ethylene-ethyl acrylate, and polyvinylpyrrolidone; the dispersant is at least one of sodium dodecyl sulfate, sodium polyacrylate, polyethylene glycol, ammonium polyacrylate, BYK182, and Texaphor 963S.

[0015] Furthermore, the porosity of the porous cement membrane is 50%~80%, preferably 53%~75%; the pore size distribution range is 2nm~600μm, preferably 3nm~200μm.

[0016] Secondly, this application provides a method for preparing a porous cement membrane, which adopts the following technical solution: A method for preparing a porous cement membrane includes the following steps: The functional modified polymer, dispersant, and binder are added to deionized water, mixed evenly, and then cement is added. The mixture is then ball-milled to obtain a uniform and stable cement-based slurry. The cement-based slurry is then subjected to directional freeze-molding, freeze-dried, and finally cured to obtain a porous cement membrane.

[0017] Furthermore, the directional freezing temperature is ~5~200℃, preferably ~15~190℃, and the freezing time is 2~20h, preferably 0.5~12h.

[0018] Furthermore, the curing operations include, in sequence: curing in a constant temperature and humidity chamber with a curing temperature ≥20℃ and humidity ≥98% for 1~7 days; and curing in a curing pool with a curing temperature ≥20℃ for 21~27 days.

[0019] In summary, this application has the following beneficial effects: 1. The porous cement membrane of this application introduces functional structures such as phosphate groups and chitosan quaternary ammonium salts through chemical means, which have excellent hydrophilicity, antibacterial properties, cationic adsorption and antistatic properties, while avoiding the mechanical property differences caused by traditional physical blending methods. It can be used in water treatment, pollution remediation, antibacterial materials and other fields.

[0020] 2. This application utilizes a combination of typical "natural growth" and "artificial induction" methods to form a directional lamellar pore structure within the cement membrane. The intrinsic properties of cement hydration products provide the basis for this lamellar structure, while the addition of functionally modified polymers is key to achieving a highly ordered, regularized structure and optimized performance. This allows for precise control over the final microstructure and macroscopic properties of cement-based materials, thereby meeting the demands of various demanding engineering applications. Detailed Implementation

[0021] The present application will be further described in detail below with reference to preparation examples and embodiments.

[0022] Preparation Example The preparation examples in this application provide a method for preparing functionally modified polymers, including the following steps: In anhydrous ethanol, tertiary ammonium acrylates and halo acids are quaternized in proportion. After reacting at 45-75℃ for 4-8 hours, the mixture is cooled to room temperature, the solvent is removed, and the mixture is washed and dried to obtain a quaternary ammonium salt cationic monomer containing a carboxyl group. A quaternary ammonium salt cationic monomer containing a carboxyl group was mixed with 1,2-dichloroethane, and hydrogen chloride gas was introduced. The mixture was reacted at room temperature for 0.5-4 hours. Chitosan was then added to the above reaction mixture, and hydrogen chloride was slowly introduced. The mixture was heated to reflux, and the azeotrope of dichloroethane and water was distilled off at 45-83°C. The mixture was separated into layers in a water separator, and the lower layer of 1,2-dichloroethane was added back into the reaction system. The reaction was completed in 4-8 hours. The mixture was cooled and filtered, and the filter cake was recrystallized to obtain a compound containing quaternary ammonium salt cationic and chitosan structures. A compound containing quaternary ammonium salt cations and chitosan structure was added to methanesulfonic acid. Then, phosphorus pentoxide was added under reaction conditions of 0-5°C, and the reaction was mechanically stirred for 2-4 hours under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether, washed, filtered, and vacuum dried at 60-80°C for 12-24 hours to obtain the functional modified polymer.

[0023] Among them, the tertiary ammonium acrylates are dimethylaminoethyl acrylate, propyl 3-(dimethylamino)acrylate, or butyl 3-(dimethylamino)acrylate; the haloacids are bromopropionic acid, bromobutyric acid, chloropropionic acid, or chlorobutyric acid.

[0024] Furthermore, taking dimethylaminoethyl acrylate as an example of a tertiary ammonium acrylate, the structural formula of the functional modified polymer is shown in Formula 1: (1) The value of N is 1-100.

[0025] The following explanation is provided through specific examples.

[0026] Preparation Example 1 This preparation example provides a functional modified polymer and its preparation method, as detailed below: (1) Preparation of small monomer a containing quaternary ammonium salt cation: A certain amount of anhydrous ethanol was added to a three-necked flask equipped with a reflux condenser and a stirrer. 172.9 g (1.1 mol) of 3-(dimethylamino)acrylate and 335.7 g (2.01 mol) of bromobutyric acid were quaternized. After reacting at 45 °C for 4 h, the mixture was cooled to room temperature. The solvent was removed by vacuum distillation at 60 °C. The mixture was then washed three times with ethyl acetate and acetone, filtered, and dried under vacuum at 45 °C to obtain small monomer a.

[0027] (2) Preparation of compound b containing quaternary ammonium salt cation and chitosan structure: 116.7 g (0.36 mol) of the small monomer a1 synthesized in step (1) and 1,2-dichloroethane were put into a three-necked flask and hydrogen chloride gas (purity 99.99%) was introduced. The reaction was carried out at room temperature for 0.5 h. Then 116.1 g (0.72 mol) of chitosan was added to the above reaction mixture and hydrogen chloride was slowly introduced. The temperature was raised to reflux, and the azeotrope of dichloroethane and water was distilled off at 45 °C. The mixture was separated into layers in a water separator. The lower layer of 1,2-dichloroethane was added back into the reaction system. The reaction was completed in 4 h. The mixture was cooled to ~15 °C, filtered, and the filter cake was recrystallized from methanol to obtain compound b.

[0028] (3) Preparation of functional modified polymer containing quaternary ammonium salt cation and phosphate group: 100.9g (0.21mol) of compound b synthesized in step (2) was added to 6ml of methanesulfonic acid. Then, under the reaction conditions of 0~5°C, 42.58g (0.3mol) of phosphorus pentoxide was added. The reaction was mechanically stirred for 2h under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether. Then, it was washed with acetone, methanol and diethyl ether respectively, filtered, and dried under vacuum at 60°C for 12h to obtain the functional modified polymer, N=55.

[0029] Preparation Example 2 This preparation example provides a functional modified polymer and its preparation method, as detailed below: (1) Preparation of small monomer a containing quaternary ammonium salt cation: A certain amount of anhydrous ethanol was added to a three-necked flask equipped with a reflux condenser and a stirrer. 157.5 g (1.1 mol) of dimethylaminoethyl acrylate and 307.47 g (2.01 mol) of bromopropionic acid were quaternized. After reacting at 45 °C for 4 h, the mixture was cooled to room temperature. The solvent was removed by vacuum distillation at 60 °C. The mixture was then washed three times with ethyl acetate and acetone, filtered, and dried under vacuum at 45 °C to obtain small monomer a.

[0030] (2) Preparation of compound b containing quaternary ammonium salt cation and chitosan structure: 106.6 g (0.36 mol) of the small monomer a synthesized in step (1) and 1,2-dichloroethane were added to a three-necked flask, and hydrogen chloride gas (purity 99.99%) was introduced. The reaction was carried out at room temperature for 0.5 h. Then, 116.1 g (0.72 mol) of chitosan was added to the above reaction mixture, and hydrogen chloride was slowly introduced. The temperature was raised to reflux, and the azeotrope of dichloroethane and water was distilled off at 45 °C. The mixture was separated into layers in a water separator. The lower layer of 1,2-dichloroethane was added back to the reaction system. The reaction was completed in 4 h. The mixture was cooled to ~15 °C, filtered, and the filter cake was recrystallized from methanol to obtain compound b. (3) Preparation of functional modified polymer containing quaternary ammonium salt cation and phosphate group: 155.23g (0.26mol) of compound b synthesized in step (2) was added to 8ml of methanesulfonic acid. Then, under the reaction conditions of 0~5°C, 42.58g (0.3mol) of phosphorus pentoxide was added. The reaction was mechanically stirred for 2.5h under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether. Then, it was washed with acetone, methanol and diethyl ether respectively, filtered, and dried under vacuum at 65°C for 14h to obtain functional modified polymer N=55.

[0031] Preparation Example 3 This preparation example provides a functional modified polymer and its preparation method, as detailed below: (1) Preparation of small monomer a containing quaternary ammonium salt cation: A certain amount of anhydrous ethanol was added to a three-necked flask equipped with a reflux condenser and a stirrer. 186.1 g (1.3 mol) of dimethylaminoethyl acrylate and 379.9 g (3.1 mol) of chlorobutyric acid were quaternized. After reacting at 45 °C for 4 h, the mixture was cooled to room temperature. The solvent was removed by vacuum distillation at 60 °C. The mixture was then washed three times with ethyl acetate and acetone, filtered, and dried under vacuum at 45 °C to obtain small monomer a.

[0032] (2) Preparation of compound b containing quaternary ammonium salt cation and chitosan structure: 199.3 g (0.75 mol) of the small monomer a synthesized in step (1) and 1,2-dichloroethane were put into a three-necked flask, and hydrogen chloride gas (purity 99.99%) was introduced. The reaction was carried out at room temperature for 0.5 h. Then 141.9 g (0.88 mol) of chitosan was added to the above reaction mixture, and hydrogen chloride was slowly introduced. The temperature was raised to reflux, and the azeotrope of dichloroethane and water was distilled off at 45 °C. The mixture was separated into layers in a water separator. The lower layer of 1,2-dichloroethane was added back into the reaction system. The reaction was completed in 4 h. The mixture was cooled to ~15 °C, filtered, and the filter cake was recrystallized from methanol to obtain compound b.

[0033] (3) Preparation of functional modified polymer containing quaternary ammonium salt cation and phosphate group: 316.15g (0.75mol) of compound b synthesized in step (2) was added to 10ml of methanesulfonic acid. Then, under the reaction conditions of 0~5°C, 141.94g (1.0mol) of phosphorus pentoxide was added. The reaction was mechanically stirred for 3h under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether. Then, it was washed with acetone, methanol and diethyl ether respectively, filtered, and dried under vacuum at 700°C for 20h to obtain functional modified polymer N=60.

[0034] Preparation Example 4 This preparation example provides a functional modified polymer and its preparation method, as detailed below: (1) Preparation of small monomer a containing quaternary ammonium salt cation: A certain amount of anhydrous ethanol was added to a three-necked flask equipped with a reflux condenser and a stirrer. 181.5 g (1.06 mol) of 3-(dimethylamino)acrylate and 229.0 g (2.11 mol) of chloropropionic acid were quaternized according to a certain ratio. After reacting at 45 °C for 4 h, the mixture was cooled to room temperature. The solvent was removed by vacuum distillation at 60 °C. The mixture was then washed three times with ethyl acetate and acetone, filtered, and dried under vacuum at 45 °C to obtain small monomer a.

[0035] (2) Preparation of compound b containing quaternary ammonium salt cation and chitosan structure: 167.84 g (0.6 mol) of small monomer a synthesized in step (1) and 1,2-dichloroethane were put into a three-necked flask and hydrogen chloride gas (purity 99.99%) was introduced. The reaction was carried out at room temperature for 0.5 h. Then 145.08 g (0.9 mol) of chitosan was added to the above reaction mixture and hydrogen chloride was introduced slowly. The temperature was raised to reflux and the azeotrope of dichloroethane and water was distilled off at 45 °C. The mixture was separated into layers in a water separator. The lower layer of 1,2-dichloroethane was added back into the reaction system and the reaction was completed in 4 h. The mixture was cooled to ~15 °C, filtered, and the filter cake was recrystallized with methanol to obtain compound b.

[0036] (3) Preparation of functional modified polymer containing quaternary ammonium salt cation and phosphate ester group: 273.99g (0.65mol) of compound b synthesized in step (2) was added to 11ml of methanesulfonic acid. Then, under the reaction conditions of 0~5°C, 127.75g (0.9mol) of phosphorus pentoxide was added. The reaction was mechanically stirred for 3.5h under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether. Then, it was washed with acetone, methanol and diethyl ether respectively, filtered, and dried under vacuum at 80°C for 21h to obtain functional modified polymer N=80.

[0037] Preparation Example 5 This preparation example provides a functional modified polymer and its preparation method, as detailed below: (1) Preparation of small monomer a containing quaternary ammonium salt cation: A certain amount of anhydrous ethanol was added to a three-necked flask equipped with a reflux condenser and a stirrer. 193.3 g (1.35 mol) of dimethylaminoethyl acrylate and 417.5 g (2.5 mol) of bromobutyric acid were quaternized. After reacting at 45 °C for 4 h, the mixture was cooled to room temperature. The solvent was removed by vacuum distillation at 60 °C. The mixture was then washed three times with ethyl acetate and acetone, filtered, and dried under vacuum at 45 °C to obtain small monomer a.

[0038] (2) Preparation of compound b containing quaternary ammonium salt cations and chitosan structure: 198.5 g (0.64 mol) of the small monomer a synthesized in step (1) and 1,2-dichloroethane were added to a three-necked flask, and hydrogen chloride gas (purity 99.99%) was introduced. The reaction was carried out at room temperature for 0.5 h. Then, 161.2 g (1 mol) of chitosan was added to the above reaction mixture, and hydrogen chloride was slowly introduced. The temperature was raised to reflux, and the azeotrope of dichloroethane and water was distilled off at 45 °C. The mixture was separated into layers in a water separator, and the lower layer of 1,2-dichloroethane was added back to the reaction system. The reaction was completed in 4 h. The mixture was cooled to ~15 °C, filtered, and the filter cake was recrystallized from methanol to obtain compound b. 3 (3) Preparation of functional modified polymer containing quaternary ammonium salt cation and phosphate group: 155.97g (0.37mol) of compound b synthesized in step (2) was added to 12ml of methanesulfonic acid. Then, under the reaction conditions of 0~5°C, 92.26g (0.65mol) of phosphorus pentoxide was added. The reaction was mechanically stirred for 4h under nitrogen atmosphere. After the reaction was completed, the product was precipitated with diethyl ether. Then, it was washed with acetone, methanol and diethyl ether respectively, filtered, and dried under vacuum at 80°C for 24h to obtain functional modified polymer N=100.

[0039] Example Example 1 This embodiment provides a porous cement membrane and its preparation method, as detailed below: 7.1 g of functionalized modified polymer (from Preparation Example 1), 0.5 g of sodium dodecyl sulfate, and 0.5 g of polyvinylpyrrolidone (molecular weight 40,000) were dissolved in 50 g of deionized water and mechanically stirred at 150 r / min for 1 h to obtain a homogeneous mixed solution. This solution was then mixed with 41.9 g of silicate cement and placed in a stainless steel ball mill jar. The mixture was ball-milled for 24 h at 200 r / min using zirconium oxide as the milling medium to obtain a homogeneous cement-based slurry. The slurry was then degassed in a vacuum drying oven, and the degassed slurry was then injected into a self-contained container. Directional cryogenic molding was performed in a mold at a freezing temperature of ~80℃ for 1 hour. After the slurry was frozen solid, the blank was removed from the mold and placed in a freeze dryer at ~50℃ for 24 hours under a vacuum of 9.2 Pa to obtain a porous cement blank. The porous cement blank was then placed in a constant temperature and humidity chamber for preliminary curing at a temperature of 20℃ and a humidity of 99% for 3 days. After curing, it was removed and placed in a curing tank containing deionized water at a temperature of 20℃ for 25 days. After curing, the sample was rinsed with an aqueous solution containing 50% ethanol for 1 hour to obtain a porous cement membrane.

[0040] Example 2 This embodiment provides a porous cement membrane and its preparation method, as detailed below: 7.5g of functional modified polymer (from Preparation Example 2), 0.3g of polyethylene glycol, and 0.7g of carboxymethyl cellulose (molecular weight 100,000) were dissolved in 52.5g of deionized water and mechanically stirred at 200 rpm for 2 hours to obtain a homogeneous mixed solution. This solution was then mixed with 39g of pozzolanic silicate cement and placed in a stainless steel ball mill jar. The mixture was ball-milled for 12 hours at 350 rpm using silicon nitride as the milling medium to obtain a homogeneous cement-based slurry. The slurry was then degassed in a vacuum drying oven. The degassed slurry was then injected into a self-made mold for directional freeze-drying at ~10℃ for 12 hours. After the slurry was frozen solid, the green body was removed from the mold and freeze-dried in a freeze dryer at ~80℃ for 26 hours at a vacuum degree of 1. 0.5 Pa was applied to obtain a porous cement blank. The porous cement blank was placed in a constant temperature and humidity chamber for initial curing at a temperature of 25℃ and a humidity of 98%. After curing for 5 days, it was removed and placed in a curing tank containing deionized water at a temperature of 25℃. After curing for 23 days, it was removed and rinsed with an aqueous solution containing 30% ethanol for 3 hours to obtain a porous cement membrane.

[0041] Example 3 This embodiment provides a porous cement membrane and its preparation method, as detailed below: 7.7g of functionally modified polymer (from Preparation Example 3), 0.9g of Texaphor 963S, and 0.1g of polyvinyl alcohol (molecular weight 67000) were dissolved in 50g of deionized water and mechanically stirred at 300r / min for 5h to obtain a homogeneous mixed solution. This solution was then mixed with 41.3g of fly ash silicate cement and placed in a stainless steel ball mill jar. The mixture was ball-milled for 20h at 400r / min using zirconium oxide as the milling medium to obtain a homogeneous cement-based slurry. This slurry was then placed in a vacuum drying oven for vacuum degassing. The degassed slurry was then injected into a self-made mold for directional freeze-drying at ~196℃ for 0.5h. After the slurry had solidified, the green body was removed from the mold and freeze-dried in a freeze dryer at ~50℃ for 48h under a vacuum of 3. 0.2 Pa was applied to obtain a porous cement blank. The porous cement blank was placed in a constant temperature and humidity chamber for initial curing at a temperature of 20°C and a humidity of 100%. After curing for 7 days, it was removed and placed in a curing tank containing deionized water at a temperature of 20°C. After curing for 21 days, it was removed and rinsed with an aqueous solution containing 60% ethanol for 2 hours to obtain a porous cement membrane.

[0042] Example 4 This embodiment provides a porous cement membrane and its preparation method, as detailed below: 7.8 g of functional modified polymer (from Preparation Example 4), 0.6 g of BYK182, and 0.4 g of polyvinyl alcohol were dissolved in 59.2 g of deionized water and mechanically stirred at 300 r / min for 5 h to obtain a homogeneous mixed solution. This solution was then mixed with 32 g of slag silicate cement and placed in a stainless steel ball mill jar. The mixture was ball-milled for 12 h at 250 r / min using stainless steel as the milling medium to obtain a homogeneous cement-based slurry. The slurry was then degassed in a vacuum drying oven. The degassed slurry was then injected into a self-made mold for directional freeze-drying at ~60℃ for 2 h. After the slurry was frozen solid, the green body was removed from the mold and freeze-dried in a freeze dryer at ~80℃ for 24 h at a vacuum degree of 2. 0.7 Pa was applied to obtain a porous cement blank. The porous cement blank was placed in a constant temperature and humidity chamber for initial curing at a temperature of 25°C and a humidity of 95%. After curing for 1 day, it was removed and placed in a curing tank containing deionized water at a temperature of 25°C. After curing for 27 days, it was removed and rinsed with an aqueous solution containing 40% ethanol for 5 hours to obtain a porous cement membrane.

[0043] Example 5 This embodiment provides a porous cement membrane and its preparation method, as detailed below: 8g of functional modified polymer (Preparation Example 5), 0.8g of ammonium polyacrylate, 0.1g of carboxymethyl cellulose, and 0.1g of polyvinylpyrrolidone were dissolved in 50g of deionized water and mechanically stirred at 100r / min for 3h to obtain a homogeneous mixed solution. This solution was then mixed with 41g of composite silicate cement and placed in a stainless steel ball mill jar. The mixture was ball-milled for 24h at 400r / min using agate as the milling medium to obtain a homogeneous cement-based slurry. The slurry was then degassed in a vacuum drying oven. The degassed slurry was then injected into a self-made mold for directional freeze-drying at ~80℃ for 1h. After the slurry was frozen solid, the green body was removed from the mold and freeze-dried in a freeze dryer at ~50℃ for 36h under a vacuum of 8... 0.3 Pa was applied to obtain a porous cement blank. The porous cement blank was placed in a constant temperature and humidity chamber for initial curing at a temperature of 37°C and a humidity of 100%. After curing for 3 days, it was removed and placed in a curing tank containing deionized water at a temperature of 37°C. After curing for 25 days, it was removed and rinsed with an aqueous solution containing 50% ethanol for 1 hour to obtain a porous cement membrane.

[0044] Comparative Example Comparative Example 1 Comparative Example 1 provides a method for preparing a cement membrane, comprising the following steps: 7.1g of commercially available unmodified chitosan (molecular weight 200,000 Da), 0.5g of sodium dodecyl sulfate, and 0.5g of polyvinylpyrrolidone were dissolved in 50g of deionized water and mechanically stirred at 150 rpm for 1 hour to obtain a homogeneous mixed solution. This solution was then mixed with 41.9g of silicate cement and placed in a stainless steel ball mill jar. The mixture was ball-milled for 24 hours at 200 rpm using zirconium oxide as the milling medium to obtain a homogeneous cement-based slurry. The slurry was then degassed in a vacuum drying oven, and the degassed slurry was injected into a self-made mold for directional cryogenic molding. The freezing temperature was 80℃, and the freezing time was 1 hour. After the slurry was frozen solid, the blank was removed from the mold and placed in a freeze dryer at 50℃ for 24 hours with a vacuum degree of 9.2 Pa to obtain a porous cement blank. The above porous cement blank was placed in a constant temperature and humidity chamber for preliminary curing at a curing temperature of 20℃ and a humidity of 99% for 3 days. After curing, it was taken out and placed in a curing tank containing deionized water at a temperature of 20℃ for 25 days. After curing, it was taken out and rinsed with an aqueous solution containing 50% ethanol for 1 hour to obtain a porous cement membrane.

[0045] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in the preparation of the functional polymer in Comparative Example 2, the raw material 3-(dimethylamino)acrylate in steps (1) and (2) is replaced with an equimolar amount of a non-tertiary amine substance, specifically hydroxyethyl methacrylate. Hydroxyethyl methacrylate contains active double bonds and hydroxyl groups, but does not contain tertiary amine groups, and therefore cannot undergo quaternization reaction.

[0046] (1) Preparation of small monomer a' without tertiary amine group: In a three-necked flask equipped with a reflux condenser and a stirrer, an equal volume of anhydrous ethanol as in Example 1 was added. Then, hydroxyethyl methacrylate and bromopropionic acid were added to the reaction system in the same molar ratio as in Example 1 (tertiary ammonium acrylate and haloacid). The reaction was stirred at 45°C for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and the solvent was removed by vacuum distillation at 60°C. The resulting product was washed three times with ethyl acetate and acetone, filtered, and dried under vacuum at 45°C to obtain the small monomer a', which does not contain a quaternary ammonium salt structure. This product contains only carboxyl and hydroxyl groups and cannot form a quaternary ammonium salt cation.

[0047] (2) Preparation of chitosan compound b' without quaternary ammonium salt cations: The monomer a' synthesized in step (1) was added to a three-necked flask with 1,2-dichloroethane, and hydrogen chloride gas (99.99% purity) was introduced. The mixture was reacted at room temperature for 0.5 to 4 hours. Then, an equal amount of chitosan as in Example 1 was added to the above reaction mixture, and hydrogen chloride was slowly introduced. The mixture was heated to reflux, and the azeotrope of dichloroethane and water was distilled off at 45°C. The reaction was completed in 4 hours. The mixture was cooled to -15°C and filtered. The filter cake was recrystallized from methanol to obtain chitosan compound b' which does not contain quaternary ammonium cations.

[0048] (3) Preparation of phosphorylated compound c' without quaternary ammonium salt cation: Compound b' synthesized in step (2) was added to an equal amount of methanesulfonic acid as in Example 1. Then, under reaction conditions of 0-5°C, an equal amount of phosphorus pentoxide as in Example 1 was added, and the reaction was mechanically stirred under nitrogen for 2-4 hours. After the reaction was completed, the product was precipitated with diethyl ether, then washed with acetone, methanol, and diethyl ether respectively, filtered, and dried under vacuum at 60-80°C for 12-24 hours to obtain compound c', which contains only phosphate groups and does not contain quaternary ammonium salt cations.

[0049] (4) Preparation of cement membrane in Comparative Example 2: The raw materials used were compound c' synthesized in step (3) at a mass percentage of 7.5%, dispersant (sodium polyacrylate) at 0.5%, binder (polyvinyl alcohol) at 0.5%, cement powder (silicate cement) at 45%, and deionized water at 46.5%. Following the process parameters of the example, subsequent steps included mechanical stirring, ball milling, vacuum degassing, directional freeze molding, freeze drying, constant temperature and humidity curing, and curing in a curing tank. After curing, the membrane was rinsed and cleaned with a 50% ethanol aqueous solution for 3 hours, ultimately yielding the porous cement membrane of Comparative Example 2.

[0050] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that, in the preparation of the functional polymer, a chitosan with a degree of polymerization (N value) much higher than 100 was used, specifically n=300, to replace the chitosan with an N value in the range of 1-100 used in Example 1. The amount of this high-degree-of-polymerization chitosan added was kept consistent with the molar ratio of other monomers in Example 1.

[0051] The specific steps for preparing the cement membrane in Comparative Example 3 are as follows: (1) Preparation of small monomer a containing quaternary ammonium salt cation: Using propyl 3-(dimethylamino)acrylate and bromopropionic acid as raw materials, a small monomer a containing a carboxyl group was synthesized. The reaction process steps were the same as in Example 1.

[0052] (2) Preparation of compound b containing quaternary ammonium salt cation and chitosan structure: The monomer a synthesized in step (1) and chitosan (n=300) are subjected to esterification reaction to generate compound b. The molar amount of chitosan (n=300) is the same as that of chitosan in Example 1, and the specific process steps are also the same.

[0053] (3) Preparation of functionalized polymers containing quaternary ammonium salt cations and phosphate groups: This step is exactly the same as in Example 1. The compound b synthesized in step (2) is reacted with phosphorus pentoxide in the same molar amount as in Example 1 to obtain the ultra-high degree of polymerization functional modified polymer c.

[0054] (4) Preparation of cement membrane in Comparative Example 3: The functional modified polymer in Example 1 was replaced with an equal amount of compound c synthesized in step (3), and the preparation process of Example 1 was followed to finally obtain the porous cement membrane of Comparative Example 3.

[0055] Performance testing The following performance tests were conducted on the cement membranes obtained in the examples and comparative examples: (1) Porosity: The Archimedes method (liquid immersion method) was used for detection; (2) Water contact angle: The static contact angle measuring instrument was used for testing. The specific process is as follows: The surface of the porous cement membrane sample is smoothed, cleaned, and dried. A drop of ultrapure water (typically 2-5 μL) is added to the sample surface using a microsyringe. A static image of the droplet on the solid surface is captured using the instrument's high-speed camera. The image is analyzed using the instrument's built-in software (such as Young-Laplace fitting or tangent analysis) to calculate the contact angle between the droplet and the solid surface. Measurements are taken at least five times at different locations on the sample, and the average value is used as the final result. A smaller contact angle indicates better hydrophilicity.

[0056] (3) Antibacterial rate: The test method is the shaking bottle method (refer to JIS Z 2801 / ISO 22196 standard).

[0057] (4) Cation adsorption capacity, which was detected by static adsorption experiment, specifically adsorption of heavy metal ions Pb 2+ The steps are as follows: 1. Prepare a series of metal ion solutions (such as lead nitrate solution) with known initial concentrations (C0).

[0058] 2. Take a certain volume (V) of solution and add a certain mass (m) of porous cement membrane sample.

[0059] 3. Shake in a constant temperature shaker until adsorption reaches equilibrium (determined by periodically sampling and measuring the concentration until it remains constant).

[0060] 4. Separate the solution and sample by filtration using a filter membrane, and measure the equilibrium concentration (Ce) of the solution using atomic absorption spectrometry or inductively coupled plasma atomic absorption spectrometry.

[0061] Calculation formula: Adsorption capacity = (C0) Ce)×V / m The adsorption capacity is usually expressed in mg / g, which represents the mass of metal ions adsorbed by each gram of adsorbent (porous cement membrane). (5) Compressive strength: Tested using a universal testing machine. The procedure is as follows: Cut the sample into regular cubes or cylinders (e.g., 10 mm × 10 mm × 10 mm). Place it between the two parallel pressure plates of the testing machine and apply pressure at a constant rate (e.g., 1 mm / min) until the sample is crushed.

[0062] Output result: compressive strength (σ, unit: MPa), calculated by the formula σ = F / A, where F is the maximum failure load and A is the cross-sectional area of ​​the sample.

[0063] The test results for the above performance are shown in Table 1.

[0064] Table 1 Performance Test Tables for Examples and Comparative Examples As shown in Table 1, the cement membrane prepared by this invention achieves high compressive strength while maintaining excellent permeability due to its high porosity. This indicates that the material possesses superior mechanical structural efficiency. The reason for this is that the polymer containing phosphate-containing chitosan quaternary ammonium salt, introduced through chemical bonding, not only acts as a reinforcing phase itself, but more importantly, its phosphate groups react with calcium ions (CaO) in the cement hydration products. 2+ Complexation occurs, optimizing the cement hydration process and forming a strong interfacial bond between the polymer fibers and the inorganic cement matrix. This strong interfacial bond tightly 'welds' the lamellar pore walls formed by directional freezing together, thereby constructing a robust mechanical network within the complex porous structure. Comparative Example 1 uses physically blended unmodified chitosan, which has a lower porosity, but its compressive strength is far lower than any embodiment of the present invention. This demonstrates that the physical blending method introduces structural defects, disrupts the continuity of the cement matrix, and leads to a significant deterioration in mechanical properties. Simultaneously, the water contact angle of the embodiment is much smaller than that of the comparative example, and the antibacterial rate and cationic adsorption are higher, indicating that the cement membrane of the present invention has superior hydrophilicity, antibacterial properties, and adsorption capacity.

[0065] Analysis of the performance of Comparative Example 2 revealed that its antibacterial rate dropped significantly to less than 60%, far lower than the 99% of Example 1. This indicates that the material lost its effective contact antibacterial ability due to the lack of quaternary ammonium salt cations. Regarding cation adsorption, Comparative Example 2 showed significantly lower adsorption for Pb... 2+ The adsorption capacity was approximately 95 mg / g, significantly lower than the 200 mg / g of Example 1. This demonstrates that the quaternary ammonium cation plays a crucial role in enhancing the cation adsorption capacity through synergistic interaction with the phosphate group. Regarding hydrophilicity, the water contact angle of Comparative Example 2 was approximately 65°, exhibiting better hydrophilicity than the unmodified pure cement membrane, but inferior to Example 1 (30°). This is because the introduced phosphate and hydroxyl groups provide hydrophilicity, but lack the superhydrophilic effect inherent in zwitterionic structures.

[0066] Comparative tests of the cement membrane obtained in Comparative Example 3 and Example 1 revealed the following: Regarding slurry compatibility and pore structure, a significant phase separation tendency was observed during the ball milling process for preparing the cement-based slurry, indicating poor compatibility between compound c and the cement slurry. After freeze-drying, the pore structure showed significant collapse and blockage, decreased orientation, and uneven pore size distribution. In terms of mechanical properties, the compressive strength of Comparative Example 3 was approximately 8.5 MPa, significantly lower than the 18.5 MPa of Example 1. This is because the ultra-high degree of polymerization functional modified polymer structure acts as a soft phase similar to a "plasticizer" in the cement matrix, severely weakening the rigidity of the cement stone skeleton. Simultaneously, its interfacial bonding with the matrix deteriorates due to excessively long chain segments. Regarding hydrophilicity and permeability, although the ultra-high degree of polymerization chitosan structure provides strong hydrophilicity, its water flux is actually lower than that of Example 1 due to the deterioration and blockage of the pore structure. In terms of functionality, due to poor compatibility and deterioration of pore structure, the distribution of functional groups (quaternary ammonium salt, phosphate group) is uneven, and its cation adsorption capacity and antibacterial rate are slightly lower than those of Example 1.

[0067] In summary, this application introduces a functional structure through chemical means, exhibiting excellent hydrophilicity, antibacterial properties, cationic adsorption, and antistatic properties, while avoiding the mechanical property differences caused by traditional physical blending methods.

[0068] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A porous cementitious membrane, characterized in that, The raw material of the porous cement film is composed of a functional modified polymer, a dispersant, a binder, cement and water; the functional modified polymer is a polymer containing a quaternary ammonium salt cation, a phosphoric acid group and a chitosan structure; and the cement film has a directional lamellar pore structure.

2. A cellular cementitious membrane according to claim 1, wherein, The mass ratio of the functional modified polymer, the dispersant, the binder, the cement and the water is (7-8):(0.3-0.8):(0.1-0.7):(50-60):(30-42).

3. The porous cementitious membrane of claim 1, wherein, The preparation method of the functional modified polymer comprises the following steps: quaternary ammonium reaction of a tertiary amine type acrylate and a halogenated acid to generate a quaternary ammonium salt cation small monomer containing a carboxyl group; esterification reaction of the quaternary ammonium salt cation small monomer containing the carboxyl group and chitosan to generate a compound containing both a quaternary ammonium salt cation and a chitosan structure; phosphorylation reaction of the compound containing both the quaternary ammonium salt cation and the chitosan structure with phosphorus pentoxide and methyl sulfonic acid to generate the functional modified polymer.

4. A cellular cementitious membrane according to claim 3, wherein, The preparation method of the functional modified polymer comprises the following steps: quaternary ammonium reaction of a tertiary amine type acrylate and a halogenated acid to generate a quaternary ammonium salt cation small monomer containing a carboxyl group; esterification reaction of the quaternary ammonium salt cation small monomer containing the carboxyl group and chitosan to generate a compound containing both a quaternary ammonium salt cation and a chitosan structure; phosphorylation reaction of the compound containing both the quaternary ammonium salt cation and the chitosan structure with phosphorus pentoxide and methyl sulfonic acid to generate the functional modified polymer.

5. A cellular cementitious membrane according to claim 3, wherein, The tertiary amine type acrylate is one of dimethylaminoethyl acrylate, 3-(dimethylamino)propyl acrylate or 3-(dimethylamino)butyl acrylate.

6. The porous cementitious membrane of claim 1, wherein, The binder is at least one of polyvinyl alcohol, carboxymethyl cellulose, ethylene ethyl acrylate and polyvinyl pyrrolidone; and the dispersant is at least one of sodium dodecyl sulfate, sodium polyacrylate, polyethylene glycol, ammonium polyacrylate, BYK182 and Texaphor963S.

7. The porous cementitious membrane of claim 1, wherein, The porosity of the porous cement film is 50%-80%, preferably 53%-75%; and the pore size distribution range is 2nm-600μm, preferably 3nm-200μm.

8. A method of producing a porous cementitious membrane as claimed in any one of claims 1 to 7, characterised in that, The preparation method comprises the following steps: The functional modified polymer, dispersant and binder are added into deionized water, mixed uniformly, then cement is added, and then ball milling is carried out to obtain a uniform and stable cement-based slurry.

9. The production method of the production method of the porous cement film according to claim 8, characterized by, The directional freezing temperature is about 5-200 DEG C, preferably about 15-190 DEG C, and the freezing time is 2-20 h, preferably 0.5-12 h.

10. The production method of the production method of the porous cement film according to claim 8, characterized by, The curing operation includes, in sequence, curing in a constant temperature and humidity chamber at a temperature of greater than or equal to 20 DEG C and a humidity of greater than or equal to 98% for 1-7 days, and curing in a curing pool at a temperature of greater than or equal to 20 DEG C for 21-27 days.

Images